Study On The Preparation Of Imidazole Modified MCM-22 Zeolites And Its Catalytic Performance Of Methane Dehydroaromatization

Aromatic hydrocarbons are one of the most important organic intermediates in the petroleum industry.Currently,they are mainly produced through crude oil processing.In recent years,due to the rapid development of China's textile industry and the rapid expansion of the polyester industry and the refined terephthalic acid industry,the market demand for aromatics has continued to grow rapidly.On the one hand,the shortage of oil resources has affected the price of petroleum aromatics.On the other hand,China's aromatic hydrocarbons have always required large amounts of imports,and foreign dependence is high.However,the supply of petroleum aromatics has been difficult to meet the market demand for aromatics.In recent years,China is actively developing technologies such as coal-to-aromatics,supplementing petroleum aromatics,reducing the external dependence of aromatics and the impact of oil prices on the aromatics market in China.The aromatization of methane to anaerobic aromatics can convert methane directly into high-value liquid aromatics through bifunctional catalysts and produce hydrogen at the same time.It has good prospects for development,which not only increases the value of methane chemical utilization,but also helps to solve the problem of high transportation costs.The main goal of this paper is to develop the highly efficient methane dehydroaromatization catalysts for the production of aromatics.The main research works are as follows:(1)Synthesis of MCM-22 molecular sieves: Using silica sol as the silicon source,cycloheximide as the template agent,sodium metaalumina as the aluminum source,and sodium hydroxide as the alkali source,the hydrothermal synthesis method was used to prepare MCM-22 molecular sieves.,Crystallization mode,silicon to aluminum ratio,alkali to silicon ratio and mold silicon ratio on the synthesis of MCM-22 zeolite.The results show that the static synthesis of the synthetic gel at 50 °C can reduce the generation of miscellaneous crystals and obtain a good MCM-22 molecular sieve sample with a wide range of silica to alumina ratios.When synthesized under dynamic conditions,the synthesis There is a mutual constraint between the molar composition of the gel.Compared to static hydrothermal crystallization,dynamic hydrothermal crystallization can obtain MCM-22 molecular sieves with good crystallinity in a shorter time.(2)Preparation of imidazole-modified MCM-22 molecular sieve: using silica sol as a silicon source,cycloheximide as a template agent,and imidazole as an additive.Under the synthetic conditions,the preparation of MCM-22 molecular sieve with in-situ modification of imidazole and the effect of imidazole addition amount on the synthesis of MCM-22 molecular sieve.The physicochemical properties of the synthesized molecular sieves were characterized by means of FTIR,XRD,BET and NH3-TPD.The results showed that compared with the conventionally synthesized MCM-22 molecular sieves,the MCM-22-was modified in situ with imidazole as an additive.The I molecular sieve has a higher specific surface area,pore volume,and acidity.(3)Performance of imidazole-modified MCM-22 zeolite catalyst: Mo/MCM-22-I molecular sieve catalysts were prepared by incipient-wetness impregnation method method with Mo and imidazole-modified molecular sieve to study the catalyst's performance of methane aerobic aromatization.The relationship between the physicochemical properties of the catalyst and the dehydroaromatization performance of methane was studied.The catalyst performance evaluation results showed that the imidazole-modified bifunctional catalyst has higher methane dehydroaromatization reaction performance,including higher methane conversion,benzene production rate,and aromatic selectivity.